Devices and methods for modulation of bone erosion

ABSTRACT

Devices and methods for stimulation of the vagus nerve to modulate (e.g., reduce, suppress, etc.) bone erosion. Methods and apparatus for modulating bone erosion may modulate levels of Receptor Activator for Nuclear Factor κB Ligand (RANKL), and/or to modulate (increase, enhance, etc.) osteoprotegerin (OPG) and/or OPG/RANKL ratio. Devices may include electrical stimulation devices that may be implanted, and may be activated to apply current for a proscribed duration, followed by a period without stimulation.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser. No. 13/851,013, filed on Mar. 26, 2013, titled “DEVICES AND METHODS FOR MODULATION OF BONE EROSION,” now U.S. Patent Application Publication No. 2013/0253413, which claims priority to U.S. Provisional Patent Application No. 61/615,777, filed on Mar. 26, 2012, and titled “DEVICES AND METHODS FOR MODULATION OF RANKL, OPG AND OPG/RANKL RATIO,” each of which is herein incorporated by reference in its entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specification are herein incorporated by reference in their entirety to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

FIELD

Described herein are devices, methods and systems to modulate bone erosion by electrical stimulation of the vagus nerve, including very low duty cycle stimulation of the vagus nerve. These systems and methods may modulate Receptor Activator for Nuclear Factor κB Ligand (RANKL), osteoprotegerin (OPG) and/or RANKL/OPG ratio by modulation of the vagus nerve. In particular, described herein are devices, methods and systems for reducing RANKL and/or increasing the RANKL/OPG ratio by stimulation of the vagus nerve.

BACKGROUND

RANKL is a member of the tumor necrosis factor (TNF) cytokine family that is a ligand for osteoprotegerin, and functions as a key factor for osteoclast differentiation, activation and survival. Targeted disruption of the related gene in mice leads to severe osteopetrosis and a lack of osteoclasts. These deficient mice exhibited defects in early differentiation of T and B lymphocytes, and fail to form lobulo-alveolar mammary structures during pregnancy.

The balance between RANKL, as a principle activator of osteoclast differentiation and activity, and its decoy ligand OPG has been shown to be the primary regulator of bone resorption. RANKL has been further validated as a mediator and biomarker of bone destruction that can be independent of coexisting cartilage damage and inflammation in arthritis.

Modulation of RANKL and/or OPG may therefore be beneficial in treatment of disorders implicated in osteoclast differentiation and/or activity, including bone regulation (e.g., resorption, remolding and/or growth). Suppression or inhibition of RANKL may be therapeutic in a range of other indications as well, including (but not limited to): glucocorticoid-induced and postmenopausal osteoporosis; reduction in bone erosions in rheumatoid arthritis, psoriatic arthritis and other systemic inflammatory diseases; increase in bone mass in patients treated with aromatase inhibitors or androgen deprivation therapy; prevention and treatment of bony metastases in solid tumors and multiple myeloma; and reduction in arterial plaque progression and rupture in atherosclerosis.

Overproduction of RANKL is implicated in a variety of bone diseases, such as rheumatoid arthritis and psoriatic arthritis. RANKL inhibitors (such as denosumab) have been proposed to treat osteoporosis in post-menopausal women. Further, inhibition of RANKL has been examined as a treatment for metastases from a variety of solid tumors and lytic bone lesions in multiple myeloma. For example, metastatic tumor cells may commandeer osteoblasts and other cells in bone to produce RANKL; the tumor cells then uses the resident osteoclasts to breakdown bone matrix and establish metastatic foci and also allow the metastases to grow.

Currently there are a number of pharmacological agents being examined to inhibit RANKL, increase OPG, or increase the OPG/RANKL ratio. For example, as mentioned above, Denosumab is an anti-RANKL antibody that inhibits RANKL. Unfortunately, there are many disadvantages to these therapies, including undesirable side effects and patient compliance. Thus, there is a need for a non-pharmacological therapy to modulate RANKL, OPG and/or OPG/RANKL ratio.

As described in detail herein, the inventors have surprisingly discovered that stimulation of the vagus nerve profoundly and significantly modulates RANKL, OPG and/or OPG/RANKL ratio. Although stimulation of the vagus nerve has been previously described, this is the first time that such stimulation (and particularly electrical stimulation) has been suggested to modulate RANKL.

For example, stimulation of the cholinergic anti-inflammatory pathway (CAP) has been shown to modulate inflammation. CAP is a physiologic regulator of systemic inflammation which utilizes the vagus nerve to reflexively reduce inflammatory responses. Brief, intermittent neurostimulation of the vagus nerve (NCAP) has been shown to be effective in a variety of animal models of acute inflammation (Nature Rev Immunol 2009; 9:418). NCAP using implantable stimulation devices also holds promise as a potential therapeutic approach for chronic human inflammatory diseases. To date, however, the biological pathways affected by NCAP have not implicated RANKL or bone morphology.

For example, US 2006/0178703 to Huston et al. describes treatment of inflammation and inflammatory disorders (including rheumatoid arthritis) by electrical stimulation of the vagus nerve. Although Huston broadly teaches the stimulation of the vagus nerve (including using an implantable stimulator), this references does not optimize the stimulation with respect to osteoprotegerin (e.g., RANKL or OPG).

By targeting the stimulation parameters specific to RANKL/OPG, the methods and devices described herein may avoid potentially undesirable and unnecessary side effects of pharmacological intervention to modulate RANKL/OPG, and may provide for the first time, an implantable, electrical or mechanical devices for modulating RANKL/OPG; non-implantable electrical and mechanical modulation means are also contemplated and described. This data has been prepared using a rodent animal model to examine the effect of vagus stimulation in a rat model, examining bone morphology generally and RANKL/OPG specifically.

SUMMARY OF THE DISCLOSURE

The present invention describes the use of stimulation (e.g., electrical stimulation) to modulate RANKL and/or OPG in a patient. In the examples described herein, a rat animal model was initially used.

As illustrated and described below, a significant reduction in RANKL as well as increases in OPG and OPG/RANKL ratio due to electrical stimulation of the vagus nerve (VNS, vagus nerve stimulation within the specific parameters described herein) is reflected in the 59% reduction in bone resorption, as compared to the sham stimulated group. The reduction in systemic RANKL and increase in OPG/RANKL ratio due to VNS therapy also has implications for protection against the systemic bone loss which often occurs in conjunction with the focal erosions characteristic of rheumatoid arthritis, especially when glucocorticoids are administered. Based on these findings, stimulation of the vagus nerve may be used to inhibit or suppress RANKL, increase OPG and/or increase a patient's OPG/RANKL ratio. Therapeutically, this type of stimulation leading to inhibition or suppression may be used to treat, prevent or ameliorate any disease or disorder for which modulation of RANKL and/or OPG would be beneficial. In particular, as taught herein, any disorder for which pharmacological suppression or inhibition of RANKL and/or OPG (e.g., using a drug such as Denosumab) would be beneficial may be treated by the modulation of the vagus nerve.

For example, described herein is the use of cuff electrodes implanted around a portion of the vagus nerve. In the rat model, cuff electrodes were implanted around the carotid sheath (encompassing the vagus nerve) of female Lewis rats. Up-regulation of RANKL was modeled (induced) as part of a protocol of rat collagen-induced arthritis (CIA). After recovery from the surgical implantation, CIA was induced with intradermal injection of bovine type II collagen and Freund's incomplete adjuvant at days (D) 0 and 6. VNS or sham stimulation was delivered once daily from D9-15 and sacrifice was on D16. Disease progression was monitored by daily caliper measurement of ankle swelling. VNS effect on histological joint damage was assessed using a semi-quantitative scoring method for inflammation, pannus formation, cartilage damage, and bone erosion, using naïve rat (n=4) joints as baseline. Serum cytokines were analyzed at D16.

As a result of this procedure, VNS significantly inhibited bone erosion in rats. Mean ankle diameter of the VNS group (n=9) was significantly lower than that of the unstimulated group (n=12) from D12-16. The average ankle swelling was reduced by 47% over this time period. VNS treatment resulted in significant improvements of all individual ankle score parameters as well as inflammation, pannus formation, and the summed histopathologic scores in knee. Surprisingly, there was a marked reduction in RANKL (80-90%) following once-daily vagus stimulation.

These data provide the first demonstration of the modulation (e.g., suppression) of bone erosion due to stimulation of the vagus nerve such as VNS, as well as the first demonstration of an effect on RANKL and/or OPG due to VNS.

Described herein are devices for modulating bone erosion by low-duty cycle stimulation of the vagus nerve. For example, a device for modulating bone erosion may include: a stimulator element configured to apply stimulation to the vagus nerve; and a controller for repeatedly applying stimulation to the vagus nerve by the stimulator element, wherein the controller is further configured to apply stimulation sufficient to modulate RANKL and/or OPG levels within the patient.

The controller may be configured to apply an extremely low duty-cycle electrical stimulation of between about 0.1 and about 10 mA to the vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours.

Any appropriate stimulator element may be used. In some variations the stimulator is a mechanical stimulator for vibrating the nerve. In some variations, the stimulator element may comprise an electrode configured to apply electrical energy to the vagus nerve. For example, the stimulator element may comprise a nerve cuff configured to apply electrical energy to the vagus nerve.

Also described are methods of reducing bone erosion in a patient at risk for bone loss. For example, the method may comprise applying stimulation to the vagus nerve to reduce RANKL level within the patient. Applying may comprise applying electrical stimulation of between about 0.1 and about 10 mA to the vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours.

The method may further comprise applying non-invasive stimulation to the vagus nerve.

In some variations the method comprises monitoring a marker related to osteoclast number, activity or number and activity. For example, the method may include determining a level of RANKL within the body.

Also described herein are methods of treating or preventing metastatic cancer comprises applying stimulation to the vagus nerve to reduce RANKL level within a patent at risk for metastatic cancer. The method may further comprise repeatedly applying an extremely low duty-cycle electrical stimulation of between about 0.1 and about 10 mA to the patient's vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours. The metastic cancer may be breast cancer, prostate cancer, myelomas, or bone cancers.

Also described are methods of treating or preventing rupture of plaques in atherosclerosis, the method comprising repeatedly applying an extremely low duty-cycle electrical stimulation of between about 0.1 and about 10 mA to the patient's vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours.

The method may also include determining a RANKL level from the patient.

Also described herein are methods of reducing bone erosion within a patient, the method comprising: repeatedly applying electrical stimulation of between about 0.1 and about 10 mA to the patient's vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours; and monitoring a marker related to osteoclast number, activity or number and activity.

In some variations, the method further comprises placing a nerve cuff around a portion of the subject's vagus nerve.

In general, monitoring the marker may comprise monitoring RANKL, OPG or RANKL and OPG.

Any of the methods described may also include administering a drug that inhibits osteoclasts. For example, the drug may be selected from the group consisting of: chloride channel inhibitors (e.g., NS3736), c-src inhibitors (e.g., AZD0530), hormones (e.g., hormone replacement therapy) and selective estrogen-receptor modulators (e.g., raloxifene, lasofoxifene, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the body weight change from day 0 in rats examined as described herein, over the 16 day period examined, in the normal control, normal control with electrode, disease control, and stimulated test groups. The fractional change between the Disease Controls and Normal Controls are expressed as percentages

FIG. 2 shows the change in rat ankle diameter over time in the normal control, normal control with electrode, disease control, and stimulated test groups.

FIG. 3 shows ankle diameter in the normal control, normal control with electrode, disease control, and stimulated test groups. The fractional change between the Disease Controls and Normal Controls are expressed as percentages

FIG. 4 shows absolute paw weight at day 16 for the normal control, normal control with electrode, disease control, and stimulated test groups. The fractional change between the Disease Controls and Normal Controls are expressed as percentages

FIG. 5 compares the ankle histopathology scores between the disease control group and the stimulation group after day 16.

FIG. 6 compares the sum of the four ankle histopathology scores between the disease control and the stimulation groups after day 16. The fractional change between the Disease Controls and Normal Controls (not shown) are expressed as percentages.

FIG. 7 compares the knee histopathology scores between the disease control group and the stimulation group after day 16.

FIG. 8 compares the sum of the four knee histopathology scores between the disease control group and the stimulation group after day 16. The fractional change between the Disease Controls and Normal Controls (not shown) are expressed as percentages.

FIG. 9A shows the significant reduction in RANKL as well as increases in OPG and OPG/RANKL ratio due to NCAP. FIG. 9B shows the concomitant significant increase in OPG.

FIG. 10A shows the dramatic difference in OPG/RANKL ratio in sham versus vagus nerve stimulation rats. Similarly FIG. 10B shows the fold-increase in OPG/RANKL ratio between sham and vagus nerve stimulated rats.

FIG. 11A illustrates one variation of a cuff electrode as described herein.

FIGS. 11B and 11C illustrate application of the cuff electrode example shown in FIG. 11A.

FIG. 11D illustrates the method of inducing the model of arthritis in rats used in some of the examples illustrated.

FIGS. 12A-D are photomicrographs of sections through the ankle regions of: (A) a normal, un-manipulated rat; (B) a normal rats in which electrodes were implanted but not stimulated; (C) disease control rats which were un-stimulated; and (D) disease rats in which NCAP (stimulation) was applied as described herein. All of these views were taken through ankle regions at 16× magnification after staining.

FIGS. 13A-D are photomicrographs of sections through the rat knee in: (A) a normal (no manipulation) knee; (B) normal rats in which electrodes were implanted; (C) rats in which arthritis (“disease”) was induced but that were not stimulated; and (D) rats in which disease was induced that were stimulated. All of these micrographs were taken at 50× after appropriate staining. FIGS. 13A and 13C are from the right knee, while 13B and 13D are from the left knee.

FIG. 14A illustrates a significant decrease in CTX/TRAP-5B compared to sham. CTX and TRAP-5B are surrogate markers for osteoclast activity (CTX), and number (TRAP-5B), respectively. FIG. 14B shows a comparison between sham and VNS rats looking at TRAP-5B, while FIG. 14C shows a comparison between sham and VNS rats examining CTX1.

FIG. 15A compares sham and VNS-treated rats for levels of Osteocalcin, a marker of bone formation.

FIG. 15B shows a comparison between sham and VNS treated rats for levels of P1NP (procollagen type 1 N-terminal peptide), another marker of bone formation.

FIG. 16 illustrates the reduction in bone erosion (bone resorption) in the animals stimulated with VNS compared to sham.

DETAILED DESCRIPTION

Described herein are methods for stimulating the vagus nerve to modulate bone erosion. These methods, devices and systems may also be used to modulate (e.g., reduce, suppress, etc.) RANKL and/or to modulate (increase, enhance, etc.) OPG. The effect of VNS as described herein, and specifically the stimulation parameters described herein, may result in a substantial reduction in bone erosion. Concurrently, the inventors have observed a reduction in RANKL and an increase in OPG compared to sham-treated animals. The modulation of bone erosion resulting from VNS described herein does not necessarily arise from the modulation of RANKL and/or OPG. However, it may also be possible to modulate OPG and/or RANKL using the device and methods described herein, which may be particularly useful in conjunction with other treatments (including pharmacological treatments) which may benefit by modulating RANKL and/or OPG.

In some variations the devices described herein are electrical stimulation devices that may be implanted, and may be activated to apply current for a proscribed duration, followed by a period without stimulation. As described in the examples that follow, the stimulation protocol may comprise a very limited period of stimulation (e.g., an on-time of less than 5 minutes, 2 minutes, 1 minute, etc.) followed by an off-time (during which stimulation is not applied, and may be prevented from being applied) of extensive duration (e.g., greater than 12 hours, greater than 20 hours, greater than 24 hours, greater than 36 hours, greater than 48 hours, etc). The applied energy may be targeted for a fixed current having a frequency that is within the range of 0.5 mA to 5 mA (e.g., approximately 3 mA), at a frequency of between about 1 Hz and about 100 Hz (e.g., 10 Hz), where the pulses applied have a pulse width of approximately (50-500 usec, e.g., a 200 usec pulse). Thus, the duty-cycle of the applied current may be extremely low, where duty cycle may refer to the ratio of on-time/(on-time plus off-time). The stimulation is applied at an extremely low duty cycle, where duty cycle may refer to the percent of on-time to the total on-time and off-time for the ongoing treatment. The effect may be seen relatively quickly, and may persist.

For example, we show herein that a low level, low duty cycle stimulation protocol (as described herein) suppresses bone erosion. Further, a low level, low duty cycle stimulation protocol (as described herein) suppresses RANKL level in blood sampled from a stimulated subject. We herein show the effectiveness of low level, low duty cycle stimulation administered over an entire week. This type of stimulation contrasts with the use of a high duty cycle stimulation used by others to modulate vagus-nerve mediated functions (such as heart rate, etc.), or treat disorders such as epilepsy and depression. An important finding here is that RANKL can be suppressed/reduced. This effect is corroborated at these low duty cycle parameters by examining the histology of the bone, showing a significant reduction in bone resorbption.

The methods, devices and systems herein may be applied specifically to treat any disorder for which a reduction or suppression of RANKL would be beneficial, including treatment of bone degeneration (e.g., rheumatoid arthritis, osteoporosis, etc.) and/or other disorders implicating bone resorption and/or osteoclasts. For example, described herein are electrodes (e.g., cuff electrodes) that may be placed around the vagus nerve and may communicate with one or more stimulators configured to apply appropriate stimulation of the vagus nerve to modulate bone erosion and/or RANKL/OPG. The stimulator may be implanted. In some variations the stimulator is integral to the electrodes, and may be charged externally. The extremely low duty-cycle of the technique described herein may allow the device to be miniaturized to a greater degree than previously suspected for the treatment of chronic disorders via an implantable device.

Example One Treatment of Rats Via Cuff Electrode

One variation of a cuff electrode (shown in FIG. 11A) was implanted in rats and compared to control animals in a model of induced arthritis. Rats were anesthetized (e.g., with intramuscular injection of Ketamine (100 mg/kg)/Xylazine (10 mg/kg)) and secured in supine position. FIGS. 11B and 11C illustrate one example of the procedure. A ventral midline cervical incision was made between the mandible and sternum. The subcutaneous tissue was dissected and retracted laterally. The mandibular salivary glands were bluntly separated and retracted laterally, and the left carotid sheath was isolated between the sternomastoid and sternohyoid muscles. A custom-built bipolar cuff electrode (illustrated in FIG. 11A) with a silicone coated platinum wire lead was secured about the carotid sheath containing the vagus nerve and tightened manually with a belt. This cuff electrode was implanted. The belt was then fastened with suture. The lead was secured to the left sternomastoid with suture, providing slack in the wire to the cuff to prevent displacement. The rat was then turned to a prone position and a 2 cm dorsal midline incision was made between the scapulae. A tunnel was created and the distal end of the electrode pulled through and positioned sub-dermally. The lead was secured to the trapezius with suture. The skin on the neck and back was sutured tightly with running suture. The rats were given subcutaneous saline for resuscitation and recovered in their cages (single rat/cage). The rats recovered from surgery for 14 days. The leads were externalized through a small incision on the back and the rats were then jacketed, securing the externalized lead. The rats acclimated to the jackets for 5 days before type II collagen arthritis treatment.

Four groups of rats were examined as part of this analysis: control (unoperated/untreated) rats, or “normal” rats; normal rats with implanted cuff electrodes; disease control rats were treated with rat collagen; and diseased treated rats, which were rats with implanted cuff electrodes that were electrically stimulated as described herein.

Group # Name Implantation CIA 1a Normal Controls N N 1b Normal Control (W/Electrodes) Y N 2 Disease Controls Y Y 3 Stimulation Y Y

Vagus nerve stimulation in animals with implanted cuff electrodes was performed after confirming the impedances between the contacts of the sheath were checked to ensure good contact and a closed circuit. Electrical stimulus was applied using a fixed current (in a range of between 0-3000 μA) at 10 Hz, 200 μsec pulse. Current was applied through the cuff electrode. These stimuli were generated by a current source stimulator running under custom software. By optimizing the level of current applied, a stimulation protocol of 3000 uA, at 10 Hz, 200 usec pulse, for 60 second duration, simulating 1×/day (e.g., on-time of 60 sec/24 hours) on the Lewis rats was used. The pulse applied was a biphasic square pulse, each phase was 200 usec, with a 50 usec interpulse duration. Voltage ranged due to constant current requirements.

In FIGS. 1-10B, the test subject animals received type II collagen arthritis treatment (intradermal injection of bovine type II collagen and Freunds incomplete adjuvant at days 0 and 6). NCAP or sham stimulation was delivered as described above (e.g., once a day for 1 min), beginning on day 9, continuing through day 15. During the course of the procedure, animals were monitored to track the effect on markers of arthritis, including ankle diameter and paw weight. After 16 days, animals were sacrificed and assayed for inflammatory markers and markers of arthritis.

Measurements of serum proteins (e.g., RANKL, OPG) were performed. Samples were measured in quadruplicate at a 2× dilution. Data shown in the figures are expressed as means or as percentage of level observed in unstimulated disease control group.

Results

As mentioned, FIGS. 1-10B illustrate the results of the animal trials at the stimulation levels described above. For example, FIG. 2 illustrates the effect of stimulation in reducing one indicator of arthritis, ankle diameter, over time. FIG. 3 shows another variation of this data, in which the change in ankle diameter is represented as a bar graph. Another indicator of arthritis is paw weight. FIG. 4 shows the effect of stimulation as described above on the absolute paw weight of the rat. There is a significant inhibition in the increase in paw weight compared to the diseased control group.

An examination of the histopathology of the control, diseased and stimulated rats was performed (e.g., see FIGS. 12A-D). A quantitative analysis of this data is shown for each of four different indices (inflammation, pannus, cartilage damage and bone resorption) in FIG. 5 comparing disease controls with rats that were stimulated as described above. Appropriate stimulation of the vagus nerve results in a significant reduction in all four of these indicators, consistent with the gross indicators described above. The final column in each cluster of columns shows bone resorption, which was significantly decreased following stimulation of the vagus nerve, as discussed above.

FIG. 6 simplifies this data, showing two bar graphs, each representing the sum of the histopathology scores. FIGS. 7, 8 and 13A-D show similar results examining the histopathology taken from the rat knee. Again, bone resorption was substantially decreased, consistent with a suppression or reduction of RANKL and/or increase in OPG as a result of electrical stimulation.

Surprisingly, vagus stimulation decreased levels of RANKL and increased levels of OPG in the serum, as shown in FIGS. 9A-10B. For example, the decrease or suppression of RANKL is directly seen when looking at levels of RANKL from blood taken from control and treated animals, as illustrated in FIG. 9A. As mentioned, receptor activator of nuclear factor κB ligand (RANKL) has a crucial role in promoting bone resorption and is antagonized by osteoprotegerin (OPG). These biomarkers have been shown to correlate with ongoing joint damage in rheumatoid arthritis. To determine whether NCAP could also result in an improvement in key clinical biomarkers of arthritis progression and therapy, terminal serum samples were analyzed for levels of RANKL and OPG. Biomarker analysis on serum RANKL and OPG was performed by ELISA (Cusabio, China) with plasma from terminal bleed according to manufacturer's specification. Samples that fell below the lower limit of detection (LLD) were assigned a value of 1 pg/ml less than the LLD (RANKL=4 pg/mL, OPG=6 pg/mL). Relative to CIA, Sham Stimulation, QD vagus nerve stimulation reduced RANKL concentration by 95% (NCAP=6±2 Vs. Sham=132±13; p=0.01) and increased OPG concentration by 145% (NCAP=44±10 Vs. Sham=18±4; p=0.02), as shown in FIGS. 9a and 9b . In addition, the OPG/RANK ratio is significantly increased in the vagus nerve stimulation group relative to the sham stimulation group (NCAP=6.8±1.3 Vs. Sham=0.1±0.1; p=0.01), representing a 54-fold increase with respect to sham, as shown in FIGS. 10a and 10 b.

As briefly described above, FIGS. 12A-D show photomicrographs taken through: the ankle of a normal control animal (FIG. 12A) (“S” indicates synovium); the ankle of a normal control animal with an electrode implanted (FIG. 12B); the ankle of a control animal in which an arthritis-like diseased state (e.g., induced by injection of collagen as illustrated in FIG. 11D and described above) has been induced (FIG. 12C); and the ankle of an animal with induced arthritis-like disease that received electrode stimulation as described above. The disease-induced ankles in FIG. 12C show marked inflammation and synovitis (S) and mild cartilage damage (large arrows) with minimal pannus (small arrows) and bone resorption (arrowhead). In contrast, the ankle from the animal that received electrical stimulation in FIG. 12D shows mild inflammation and synovitis (S) and minimal cartilage damage (large arrow) with minimal pannus (small arrows).

Similarly, FIGS. 13A-D show micrographs through sections of the knees of: a normal control animal (FIG. 13A); a normal control animal with electrode stimulation (FIG. 13B); a disease control animal (FIG. 13C); and a diseased animal that received electrode stimulation (FIG. 13D). The disease control animal showed severe inflammation and synovitis (S) and moderate cartilage damage (large arrow) with mild pannus (small arrow) and bone resorption (arrowhead). In contrast the diseases animal that received stimulation (shown in FIG. 13D) had severe inflammation and synovitis (S) and moderate cartilage damage (large arrow) with mild pannus (small arrow) and bone resorption (arrowhead).

Systems and Devices

In general, a device or system for modulating RANKL and/or OPG may include a stimulator element (e.g., an electrode, actuator, etc.) and a controller for controlling the application of stimulation by the stimulator element. A stimulator element may be configured for electrical stimulation (e.g., an electrode such as a cuff electrode, needle electrode, paddle electrode, non-contact electrode, array or plurality of electrodes, etc.), mechanical stimulation (e.g., a mechanical actuator, such as a piezoelectric actuator or the like), ultrasonic actuator, thermal actuator, or the like. In some variations the systems and/or devices are implantable. In some variations the systems and/or device are non-invasive. In general, the controller may include control logic (hardware, software, firmware, or the like) to control the activation and/or intensity of the stimulator element. The controller may control the timing (e.g., on-time, off-time, stimulation duration, stimulation frequency, etc.). In variations in which the applied energy is electrical, the controller may control the applied waveform (amplitude, frequency, burst duration/inter-burst duration, etc.). Other components may also be include as part of any of these device or system, such as a power supply (e.g., battery, inductive, etc.), transmit/receive elements (e.g., antenna, encoder/decoder, etc.), signal generator (e.g., for conditioning or forming the applied signal waveform), and the like.

In one example, an implantable device for modulating RANKL and/or OPG includes an electrode for electrically stimulating the vagus nerve. The electrode may be, for example, a cuff electrode. The electrode may be connected (directly or via a connector) to a controller and signal generator. The signal generator may be configured to provide an electrical signal to the electrode(s). For example, the electrical signal may be an electrical waveform having a frequency of between about 0.1 Hz and about 1 KHz (e.g., 10 Hz), where the pulses applied have a pulse width of approximately (50-500 usec, e.g., a 200 usec pulse). The signal generator may be battery (and/or inductively) powered, and the electrical signal may be amplitude and/or voltage controlled. For example in some variations the device or system may be configured to apply a current that is between about 0.05 mA to 25 mA (e.g., approximately 0.5 mA, 1 mA, 3 mA, etc.). The electrical signal may be sinusoidal, square, random, or the like. In generally the controller (which may be embodied in a microcontroller such as a programed ASIC), may regulate turning on and off the stimulation. For example, stimulation may be applied for an on-time of between about 0.1 sec and 10 minutes (e.g., between 1 sec and 5 minutes, between 1 sec and 2 minutes, approximately 1 minute, etc.); the stimulation may be configured to repeat automatically once every other day (off time of approximately 48 hours), once a day (e.g., with an off-time of approximately 24 hours), twice a day (off-time of approximately 12 hours), three times a day (off time of approximately 8 hours), four times a day (off time of approximately 6 hours), or the like. In some variations the implant may be configured to receive control information from a communications device. The communications device may allow modification of the stimulation parameters (including off-time, on-time, waveform characteristics, etc.).

In use, an implant may be configured to be implanted so that the electrodes contact or approximate the vagus nerve or a portion of the vagus nerve. In one variation the implant includes a cuff that at least partially surrounds the vagus (e.g., near the carotid region). The controller and/or signal generator (including any power source) may be formed as part of the cuff or may be connected to by a connector (e.g., wire).

In some variations the device may be non-invasive. For example, the device may be worn outside the body and may trigger stimulation of the vagus nerve from a site external to the body (e.g., the ear, neck, torso, etc.). A non-invasive device may include a mechanical device (e.g., configured to apply vibratory energy). In some variations the device is configured to apply ultrasound that may specifically target the vagus nerve and apply energy to activate the vagus nerve. In some variations, transcutaneous magnetic stimulation of the vagus nerve may be used.

In any of the variations described herein, the devices, system and methods may be configured to prevent desensitization of the signal in a way that would reduce or inhibit the modulation bone erosion and/or of RANKL and/or OPG. For example in some variations, “over stimulation” of the vagus nerve, e.g., simulation at intensities that are too great or applied for too long, or outside of the frequency ranges described herein, may result in desensitization of the effect, thus further modulation may be limited or inhibited.

The examples illustrated above may provide insight into the devices, systems and methods of use for stimulation of the vagus nerve to modulate bone erosion and/or RANKL and/or OPG. These methods and devices may be used to treat any indication for which modulation of osteoclasts would be beneficial. Non-limiting examples of indications include rheumatoid arthritis, osteoarthritis, psoriatic arthritis, certain cancers (e.g., breast cancer, prostate cancer, myelomas, bone cancers), atherosclerosis (e.g., to prevent rupture of atherosclerotic plaques), etc. In general, these devices may offer alternative and in some ways superior treatment as compared to pharmacological interventions aimed at modulating RANKL and/or OPG, and therefore may be used for any indication for which such pharmacological treatments are suggested or indicated.

Thus, the methods of modulating bone erosion as described herein may be used in conjunction with one or more pharmacological interventions, and particularly interventions that treat bone erosion and related disorders or conditions. The methods described herein, which have been shown to modulate RANKL and OPG, may potentiate other treatments, and particularly those that effect the activity of osteoclasts. For example, it may be beneficial to treat a subject receiving stimulation of the vagus nerve to modulate bone erosion by also providing agent such as a chloride channel inhibitors, c-src inhibitors, hormones (e.g., hormone replacement therapy) and selective estrogen-receptor modulators (SERM). As the vagal stimulation already modulates the RANKL/OPG ratio, further modulation of osteoclast differentiation may not be necessary, though in some variations agents that effect differentiation may be potentiated by this treatment.

Thus, described herein are devices (VNS devices) for the treatment of bone erosion. Such devices are generally configured to apply low duty-cycle stimulation to the vagus nerve of a subject, as described in any of the variations (or sub-combinations) of these variations.

In use, any of the methods described herein may include a step of monitoring osteoclasts, which may include osteoclast numbers and/or activity, and/or differentiation. Osteoclasts may be monitored directly (e.g., by histology, imaging, etc.) or indirectly by one or more markers correlated or correlatable with osteoclast number, genesis and/or activity, including RANKL, OPG, TRAP-5B, CTX-1, cathespsin K, or any other appropriate marker, including markers for resorption (e.g., NTX/DpD, etc.). Monitoring may be continuous or discrete (e.g., at one or more times, or time intervals).

The information described herein for the first time shows that stimulation of the vagus nerve modulates bone erosion. This is seen directly in the mouse model, as described above in FIGS. 1-5. FIG. 16 extracts the data specific to bone erosion between sham and rats receiving VNS. In FIG. 16, preserved and decalcified (5% formic acid) ankle joints were cut in half longitudinally, processed through graded alcohols and a clearing agent, infiltrated and embedded in paraffin, sectioned, and stained with Toluidine Blue (T. blue) by Bolder BioPATH, Inc. associated personnel. Tissues from all animals were examined microscopically by a board certified veterinary pathologist and observations were entered into a computer-assisted data retrieval system. In FIG. 16, the scoring of Joints Bone Resorption from the ankle was ranked as 0 (Normal), 1 (Minimal, small areas of resorption, not readily apparent on low magnification, rare osteoclasts), 2 (mild, with more numerous areas of resorption, not readily apparent on low magnification, osteoclasts more numerous, <¼ of tibia at edges is resorbed), 3 (moderate, with obvious resorption of medullary trabecular and cortical bone without full thickness defects in cortex, loss of some medullary trabeculae, lesion apparent on low magnification, osteoclasts more numerous, ¼ to ⅓ of tibia affected, smaller tarsals affected), 4 (marked, full thickness defects in cortical bone, often with distortion of profile of remaining cortical surface, marked loss of medullary bone, numerous osteoclasts, ½-¾ of tibia affected, destruction of smaller tarsals) and 5 (severe, full thickness defects in cortical bone, often with distortion of profile of remaining cortical surface, marked loss of medullary bone, numerous osteoclasts, >¾ of tibia affected, severe distortion of overall architecture).

In FIG. 16, it is clear that relatively low duty-cycle (infrequent ongoing) stimulation of the vagus nerve in the rats results in a significant reduction in bone erosion compared to sham-stimulated animals receiving the same type II collagen arthritis treatment, which otherwise results in bone erosion. Additional markers for activity of osteoclasts were also examined consisted with the modulation of bone erosion seen with VNS. For example, FIG. 14A shows the ration of CTX1/TRAP-5b from serum taken from a terminal draw (>D16) of animals undergoing the rat collagen-induced arthritis protocol (e.g., FIG. 11D). CTX1/TRAP-5B may be referred to a measure of osteoclast activity.

In FIG. 14A, the ratio of CTX1/TRAP-5b is consistent with the reduction in osteoclast activity seen in animals stimulated with VNS, compared to sham animals. FIGS. 14B and 14C illustrate the serum levels of TRAP-5b and CTX1, respectively. Serum levels of TRAP-5b is thought to be a metric for osteoclast number, but not activity. Similarly, the level of CTX1 was also examined at the same terminal blood draw, as shown in FIG. 14B. CTX1 is believed to be a measure of osteoclast activity/bone degradation. The reduction in total activity of the osteocytes is consistent with the morphological/histological data (showing less bone erosion) and with the RANL/OPG data. Although the precise mechanism of action of vagal stimulation in reducing resorption of bone by osteoclast, it is clear that VNS in the ranges descried herein significantly reduces the amount of bone erosion.

Further, stimulation of the vagus using the parameters described herein does not appear to significantly affect bone formation in the same animals. FIGS. 15A and 15B illustrate a lack of effect of VNS in the same animals examined in FIGS. 1-10B on bone formation. In FIG. 15A, the levels of Osteocalcin, a marker for bone formation, is not significantly different between sham and VNS animals. In FIG. 15B, P1NP (pro-collagen type 1 N-terminal peptide), a marker of one formation, if not significantly different between sham and VNS animals.

The examples provided herein are not intended to be comprehensive, but merely illustrate and embody certain variations of the invention. It is within the abilities of one of ordinary skill in the art to understand and apply, without undue experimentation, the invention as described herein. 

What may be claimed is:
 1. A method of reducing bone erosion in a patient at risk for bone loss, the method comprising applying stimulation to the vagus nerve to reduce RANKL level within the patient, wherein applying comprises applying electrical stimulation of between about 0.1 and about 10 mA to the vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours.
 2. The method of claim 1, further comprising applying non-invasive stimulation to the vagus nerve.
 3. The method of claim 1, further comprising monitoring a marker related to osteoclast number, activity or number and activity.
 4. The method of claim 3, further comprising determining a level of RANKL within the body.
 5. A method of reducing bone erosion within a patient, the method comprising: repeatedly applying electrical stimulation of between about 0.1 and about 10 mA to the patient's vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours; and monitoring a marker related to osteoclast number, activity or number and activity, wherein monitoring the marker comprises monitoring RANKL, OPG or RANKL and OPG.
 6. The method of claim 5, further comprising placing a nerve cuff around a portion of the subject's vagus nerve.
 7. The method of claim 5, further comprising administering a drug that inhibits osteoclasts.
 8. The method of claim 7, wherein the drug is selected from the group consisting of: chloride channel inhibitors, c-src inhibitors, hormones and selective estrogen-receptor modulators.
 9. A method of reducing bone erosion within a patient, the method comprising: repeatedly applying electrical stimulation of between about 0.1 and about 10 mA to the patient's vagus nerve for less than about 2 minutes, followed by an off-time of between about 12 and about 48 hours; monitoring a marker related to osteoclast number, activity or number and activity; and administering a drug that inhibits osteoclasts.
 10. The method of claim 9, wherein the drug is selected from the group consisting of: chloride channel inhibitors, c-src inhibitors, hormones and selective estrogen-receptor modulators. 